Slinger - Town. Appear in certain locations throughout the town.
Slinger - Quarry. Once you have made it to the top of the opposite side of the quarry, a Slinger reappears as you approach the exit gate with the power source.
Slinger - The Mines. Several appear from the caves surrounding the wooden walkway section of the area you explore to activate the door that leads you to the platform where you can switch on the ventilation system.
Slinger - Underground Research Facility - Basement. In the room that has the elevator that leads down to the final area. A Slinger appears after you have activated the elevator.